1. Field of the Invention
The present general inventive concept relates to a virtual sound reproducing system, and more particularly, to a method of reproducing a virtual sound and an apparatus to reproduce a 2-channel virtual sound from a 5.1 channel (or 7.1 channel or more) sound using a two-channel speaker system.
2. Description of the Related Art
A virtual sound reproducing system typically can provide the same surround sound effect detected in a 5.1 channel system using only two speakers.
A technology related to a conventional virtual sound reproducing system is disclosed in WO 99/49574 (PCT/AU99/00002, filed Jan. 6, 1999, entitled AUDIO SIGNAL PROCESSING METHOD AND APPARATUS). In the disclosed technology, a multi-channel audio signal is downmixed into a 2-channel audio signal using a head-related transfer function (HRTF).
FIG. 1 is a block diagram illustrating the conventional virtual sound reproducing system. Referring to FIG. 1, a 5.1 channel audio signal is input. The 5.1 channel audio signal includes a left-front channel 2, a right-front channel, a center-front channel, a left-surround channel, a right-surround channel, and a low-frequency (LFE) channel 13. Left and right impulse response functions are applied to each channel. Therefore, a left-front impulse response function 4 for a left ear is convolved with a left-front signal 3 with respect to the left-front channel 2 in a convolution operation 6. The left-front impulse response function 4 uses the HRTF as an impulse response to be received by the left ear in an ideal spike pattern output from a left-front channel speaker located at an ideal position. An output signal 7 of the convolution operation 6 is mixed into a left channel signal 10 for headphones. Similarly, in a convolution operation 8, a left-front impulse response function 5 for a right ear is convolved with the left-front signal 3 in order to generate an output signal 9 to be mixed to a right channel signal 11. Therefore, the arrangement of FIG. 1 requires 12 convolution operations for the 5.1 channel audio signal. Ultimately, if the signals included in the 5.1 channel audio signal are reproduced as 2-channel signals by combining measured HRTFs and downmixing, it is possible to obtain the same surround sound effect as when the signals in the 5.1 channel audio signal are reproduced as multi-channel signals.
However, a system for receiving a 5.1 channel (or 7.1 channel) sound input and reproducing virtual sound using a 2-channel speaker system has a disadvantage in that, since the HRTF is determined with respect to a predetermined listening position within the 2-channel speaker system, a stereoscopic sensation dramatically decreases if a listener is out of the predetermined listening position.